Electric semi-conducting devices

ABSTRACT

914,592. Semi-conductor devices. STANDARD TELEPHONES &amp; CABLES Ltd. April 17, 1959 [April 23, 1958], No. 13142/59. Class 37. [Also in Group XXII] A semi-conductor element is mounted in a casing comprising a metal part including a rim fitting into a channel in another metal part of different hardness. After assembling the parts with the rim in the channel, the housing is sealed by plastic deformation in the cold of one of the parts. In one embodiment the softer part is a threaded copper bolt 4 with an annular channel 3. Sealing is effected by deforming the edges of the channel over the flanged edge of steel cylinder 6. External connection to the upper face of the semi-conductor element is provided by a stranded copper or silver wire (Fig. 4) with a conical solid end engaging the element. The wire leaves the housing through a metal tubule 8 in a sintered glass bead 7. The wire, which is deformed and solid where it passes through the tubule, is pinch sealed therein in vacuo or in an inert atmosphere, the abutting surfaces of the wire and tube being coated with a low-melting metal, e.g., tin, to facilitate sealing. In an alternative arrangement, the wire consists of a solid-headed part 11b of silver and an upper part 11a of tinned copper, the abutting solid ends 13a, 13b having the cross-sections shown to facilitate evacuation of the housing prior to sealing. During the pinch sealing process, the two parts of the wire are joined and sealed within the tube. In a modification of the above device, the copper base is internally threaded for mounting on a cooling block and silverplated to allow etching of the mounted semiconductor element without copper contamination of the etchant. A transistor is also described, comprising two sub-assemblies 5, 6, 7, 8 of the construction shown in Fig. 1, sealed in annular grooves on opposite faces of an apertured plate carrying the semi-conductor element. In another arrangement (Fig. 3) comprising copper base-plate 4 and steel cap 2, connections are sealed through the base-plate by glass-metal seals, as shown in Fig. 3a, the edges of apertures 10 being deformed in the cold state to fix the seals.

H. WOLFSON ETAL ELECTRIC SEMI-CONDUCTING DEVICES Filed June 7. 1952 March 12, 1957 6 I 7 L i 23 9 Inventor H. WOLF SON -s.c. HEPARD 1% Attorney United States Patent-O ELECTRIC SEMI-CONDUCTING DEVICES Henry Wolfson and Stanley Carden Shepard, London, England, assignors to International Standard Electric Corporation, New York, N. Y.

Application June 7, 1952, Serial No. 292,304

Claims priority, application Great Britain June 8, 1951 4 Claims. (Cl. 317234) The present invention relates to improvements in small crystal electric rectifiers employing semiconducting materials such as germanium.

The principal object of the invention is to simplify and cheapen the construction of such rectifiers and to improve the protection of the rectifying contact against the efiects of moisture.

This object is achieved according to the invention by providing an electric rectifier comprising a body of semiconducting material and an electrode making rectifying contact therewith, assembled inside a tube of electrically insulating material, the said body and electrode being each secured to a corresponding metal plug, the said plugs being force fits inside the said tube at respectively opposite ends thereof and being spaced apart in such manner that the electrode makes rectifying contact with the semiconducting body.

T he invention will be described with reference to the accompanying drawing in which:

Fig. 1 shows a sectional view of a crystal rectifier constructed according to the present invention;

Figs. 2 to 7 show details in the process of constructing the rectifier. I

Fig. 8 shows a side view of a completed rectifier,

Figs, 9 to 12 show details of a modified type of rectifier according to the invention;

Figs. 13 to 16 show details of another form of rectifier according to the invention in which the plugs on which the electrodes are mounted are solid, instead of being pressed from sheet material.

Figs. 17 and 18 show details of a modified form of the solid plug type rectifier;

Figs. 19 and 20 show modifications of Figs. 13 and 14 respectively; and Figs. 21 and 22 show details of another modified form of the solid plug type rectifier.

:Fig. 1 shows a section through a rectifier according to the invention, in which the rectifying elements are enclosed in a cylindrical tube 1 of ceramic or other suitable insulating material, the external diameter of which might, for example be about 0.25 inch. The crystal 2, which will preferably be of germanium, and the cat whisker electrode 3, are secured to sheet metal cup-shaped plugs 4 and which are forced into opposite ends of the tube 1 in such manner as to be securely held therein. Corresponding terminal conductors 6 and 7 are attache-d to the plugs 4 and 5, and the ends of the tube are sealed with blocks 8 and 9 of a suitable thermosetting cement. A litharge-glycerine cement could be used. In order to identify the terminals of the'rectifier, the cement blocks may be differently coloured; for example, the block 8 might be red and the block 9 might be white.

,The plug 4 or 5 may be formed from a flat disc 10, of nickel or other suitable metal, shown in Fig. 2. This disc may be 0.005 inch thick, and should be slightly larger in diameter than the internal bore of the tube; for example, the diameter of the disc might be about 0.2 inch. It should be provided with a small tag 11 to which will be welded or soldered the corresponding terminal conductor 6 or 7 (Fig. 1). Other metals which might be used for the disc 10 are copper, iron, brass, or silver.

As shown in Fig. 3, the cat whisker 3, which may consist of .a sharply pointed tungsten wire :bent into the usual 8 shape, is welded or otherwise attached to the centre of the disc 10, and the assembly is arranged concentrically over the end of the tube 1. Various other metals and alloys could be used for the cat whiskers. A cylindrical ram (not shown) is applied to the centre of the disc which is thereby forced into the tube, forming a cupshaped plug, as shown in Fig. 4. The plug 5 should be pushed in leaving the tag 11 protruding as shown. The diameter of the ram should preferably be a few thousandths of an inch smaller than the inside diameter of the cup so formed, in order to avoid cracking the tube 1, and to allow the ram to be easily removed.

The terminal conductor wire 7 is welded or otherwise attached to the tag 11, as shown in Fig. 5. This terminal wire should preferably be of copper-clad steel, or of a copper-nickel-iron alloy, but other materials such as pure copper or nickel could be used. The wire 7 should preferably be arranged coaxially with the tube 1.

The cement block 9 is preferably formed from a casting resin sold under the registered trademark Araldite, though other thermosetti-ng or thermoplastic materials or other types of cement could be used. The assembly 1 should be heated to a temperature of about 250 C., for example by standing the tube 1 on a heated plate, and the casting resin in the form of a thin stick should be touched on to the upper end of the tube 1 until a sufficient quantity has melted on to fill the plug 5 and to cover the end of the tube. The resin polymerises and hardens'in about ten minutes, thereby joining the plug and tube together and efiiciently sealing the end. The resin may alternatively be applied as a powder, or in the form of a small disc with a central hole, which is of the right size to form the block 9, and which is slipped over the wire 7.

As shown in Fig. 6, the crystal 2 is attached to a second disc similar to that shown in Fig. 2, by soldering, or by means of a suitable conducting medium indicated at 12. Preferably a conducting cement of the kind described in the specification of co-pending application Serial N0. 278,527, filed March 25, 1952, should be used. The

disc bearing the crystal 2 is then forced into the open end of the tube 1, as shown in Fig. 7 by means of a ram (not shown) as previously described, and is pushed care- .fully in until contact is just made between the cat whisker electrode 3 and the crystal 2. The plug 4 is now further advanced about 0.003 inch to ensure enough pressure to guarantee mechanical stability of the contact.

' The terminal wire 6 (not shown in Fig. 7) is then attached to the tag 11, .and the plug 4 is sealed with the casting resin as described with reference to Fig. 5, the completed rectifier appearing as shown in Fig. 8. In or' der conveniently to heat the tube 1 in this case, it may be inserted into a hole in a thick metal block which rests on the hot plate.

The cement used for the cat whisker end of the tube 1 should preferably consist of a mixture of 50% of the Araldite casting resin and 50% alumina, or other white powder or pigment, which forms a white block when p-olymerised, but unfilled Araldite resin or adhesive could be used. The block at the crystal end could be formed from alumina-filled resin to which has been added a dye or pigment which might be red, or any other distinctive col-our.

The rectifier should preferably be further heat treated for 24 hours in an oven at a temperature of C. for finally hardening the sealing plugs 8 and 9.

Figs. 9 to 12 show an alternative method of attaching the cat whisker and its terminal wire to the corresponding Wish- 349 plug. As shown in Figs. 9 and 10, the plug 5 is formed from a plain disc 13 with a central hole 14 instead of a tag. The disc is rammed into the end of the tube 1 as previously described, and as shown in Fig. 10. v I V The Whisker 3 is welded to the terrninal wire 7 slidwh in Fig. 11, and also a springy wire bent into an obtuse V-shape. The wire 7 is then threaded through the hole 14 from the inside of the tube and pulled through as shown in Fig. 12, the wire 15 then holding the whisker 3 centrally inside the tube. In this case it is not neces sa-ry to solder or weld the whisker or terminal wire to the plug 5. The sealing block 9 is then applied in the manner already described.

Figs. 13 to 16 show the preferred form of the construction of a rectifier according to the invention in which the plugs to which the cat whisker and crystal are attached are formed solid from a soft metal instead or" being pressed out of sheet material. The plug for the crystal is shown in Fig. 13 and consists of a substantially cylindrical plug 16 of lead or other soft metal or alloy having a central hole into which the terminal wire 6 is fixed. Preferably the wire should be tinned and the lead plug cast or alloyed thereto forming- .a substantially brazed joint. The diameter of the plug should be very slightly larger than the inside diameter of the tube 1 and may be very slightly tapered to enable it to be started in the tube. It is then forced in with suitable ram (not shown) as before described. The thickness of the plug might for example be about 0.67 inch. The plug 17 for the cat whisker shown in Fig. 14 differs only from the other in that the terminal wire projects right through the lead plug to provide an end 18 to which the cat whisker 3 may be welded. V

Fig. 15 shows the plug 17 with the cat whisker 3 attached, and rammed into the upper end of the tube 1. Fig. 16 shows the completed rectifier with the plug 16, hearing the crystal 2, forced into the lower end, the rectiher being sealed with cement blocks 8 and 9 as previously described. The crystal 2 may be attached to the plug 16 in the manner already explained.

The material of the plugs 16 and 17 could alternatively be lead alloyed with calcium or antimony, or with tin and silver.

It will be noted that if the tube 11's composed of a nonporous glazed ceramic material, the caulking action of the soft metal will produce a good seal against ingress of moisture. The seal is further improved by the use of the Araldite resin which adheres very well both to metal and to ceramic materials, and has a low moisture absorption.

Figs; 17 and 18 show a variation 'of the method of fixing the plug for the cat whisker electrode. As shown in Fig. 17, a disc 19 of lea slightly smaller in diameter than the bore of the tube 1 is slipped inside and is pressed between two rams 2i) and 21, which should be perhaps 0.02 inch smaller in diameter thanthe inside of the tube. The lead extrudes slightly between the rams and the tube thereby locating the plug firmly in place. A small central hole is then drilled through the plug, and a cat whisker assembly similar to that shown in Fig. 11 is threaded through as shown in Fig. 18.

Figs. 19 and 20 show modifications of Figs. 13 and 14 in which the lead plug consists of two coaxial sectionsor discs, which may be separate, the upper section 22 being. slightly larger, and the lower section 23 being slightly smaller than the internal base of the tube. This facilitates centering the plugs in the tube before they are forcedin.

An alternative-method forcen'tering plugs of the type shown in Figs. 13 and 14 is shown in Figs; 21 and 22. The inside ends of the tube 1 are slightly enlarged as'indicatedat 24 and 25 in Fig. 21, the diameter of the lead plug being intermediate between the larger and smallerinternal diameters of the tube; The plug 17 after having been forced in by a ram, whose diameter is also intermediate between the larger and smaller diameters of the tube, appears as shown in Fig. 22, the lead extruding partly downwards and partly outwards and upwards round the ram (not shown). The plug (not shown) which carries the crystal can be forced into the lower end of the tube in the same manner. The ends will be sealed with the casting resin as previously described,

One of the advantages of the constructions described is the fact that no partswhich have to be accurately machined are used, arid the re'c 'tifiers are easy to assemble, no screws or solder being used in, thefinal assembly. They can be made very small and light, and can be soldered into circuits Without the necessity for special precautions to keep them cool.

While the principles of the invention have beendescribed above in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made by way of example and not as a limitation on the scope of the invennon.

What we claim is: v g

1. .An electric rectifier comprisinga body of semi-conduoting material and a wire electrode making rectifying contact therewith assembled inside a hollow tube, said body and electrode each secured to a corresponding plug, said plugs being force fits inside said tube at respectively opposite ends thereof andspaced apart whereby the electrode makes rectifying contact with the semi-conducting body, and said wire electrode connected to a terminal wire passing through a central hole cut through the base of its associated plug, the arrangement being centered by a V-shaped wire of springy material attached to said terminal wire and bearing on the inside surface of said tube.

2. An electric rectifier comprising a body of semi-conducting material and' a wire electrode making rectifying" contact therewith, assembled inside a hollow tube, the wall of said tube being under-cut at both ends to form short sections with increased internal diameter, said body and electrode each'secured to a corresponding plug, said plugs being pressed into contact with the corresponding undercut section of larger diameter and against the portion of thetube of smaller diameter, said plugs being spaced apart so that the electrode makes rectifying contact with the semi-conducting body, a terminal wire having a portion extending into the space between saidtwo'plugsandpass ing through an opening provided in one of said plugs, means for connecting said wire electrodeto' said portion of said terminal wire, and means for connecting said semiconducting body to the other of said plugs.

3. A rectifier according to claim 1, where'inlsaid tube is made of insulating material and said plugs are made of electrically conducting material.

4. A rectifier according to claim'2 in whicheach end of the said tube is sealed by a block of thermoplastic or therrriosetting material. 1

References Citedin the file of this patent 

